It has been widely accepted that calcium is an essential element for formation of bones and teeth in animals, including humans. In fact, though calcium is the most abundant mineral in the body, approximately 99% of the body's calcium is found in the bones and teeth providing an exchangeable pool of calcium. The remaining one percent is widely distributed in cells and body fluids and is responsible for the regulation of a number of metabolic functions such as nerve impulse conduction, muscle fiber contraction, hormone secretion, blood coagulation, normal heart beat, activation of enzymes, and maintenance of cell membranes. Additionally, calcium is receiving much attention on the front line of medical science because it has recently been discovered that calcium is one of the most important elements for supporting many life activities. For example, recent observations indicate that calcium deficiency not only induces osteoporosis, but also contributes to such diseases as hypertension, arteriosclerosis, arthritis, diabetes, immunological diseases, colon cancer, and obesity. Therefore, the presence of sufficient amounts of calcium within the body is essential for proper health.
Dairy products such as cream, sour cream, milk, cheese, ice cream, and yogurt and oleaginous foods such as margarine, butter, lards, and oils are important parts of our daily diet. Though the calcium content found naturally in dairy products and oleaginous foods may be acceptable if consumed at high quantities, there is great public interest in the consumption of calcium fortified dairy products and oleaginous foods that contain a relatively high percentage of stable, palatable and bioavailable calcium.
It is common practice to fortify food products with calcium sources, some of which are insoluble and some of which are soluble at or near neutral pH levels. Additionally, many of the calcium sources disclosed in the prior art for use in the fortification of dairy products and oleaginous foods are insoluble or substantially insoluble at around neutral pH including inorganic and organic acid salts of calcium. These materials result in precipitation causing a chalky feel in the mouth. Some inorganic and organic acid salts of calcium are soluble or substantially soluble at around neutral pH. However, when these salts are used to fortify products containing milk protein, undesirable coagulation and sedimentation often results.
There are also purity concerns with some of the calcium sources cited in the prior art. For example, calcium carbonate derived from bone meal, oyster shell, or other biological origin contains trace amounts of lead and other minerals. Additionally, some calcium carbonates also contain silica. Therefore, it is necessary to take additional amounts of these materials to achieve the same bioavailable calcium level as those taken from synthetic sources of essentially pure calcium.
There are several known factors which affect the absorption of calcium by the human body. Approximately 30% of the calcium contained in a healthy adult's diet is absorbed by the body. However, the absorption of calcium from various foods may range from 10% to 40%. The body's need for calcium is the most significant factor in controlling the absorption process. At very high intakes, the efficiency of calcium absorption decreases.
Another factor to consider is that many forms of ingested calcium are water insoluble and require specific enzymes for proper digestion. These enzymes extract the calcium from food and transport it into the blood stream. However, these transport enzymes are not 100% efficient. This means that the transfer of calcium into the blood stream is at an amount that is less than the total ingested calcium.
On the other hand, biological transport of calcium may be enhanced when the calcium is bound in a chelate structure comprised of calcium and an amino acid. In the area of animal nutrition, the American Association of Feed Control Officials has officially defined an amino acid chelate as "a metal ion from a soluble salt with amino acids with a mole ratio of one mole of metal to one to three (preferably two) moles of amino acids to form coordinate covalent bonds. The average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of chelate must not exceed 800."
It is known in the art that amino acid chelates show enhanced bioavailability as compared to non-chelated minerals. Moreover, it is also known that this increased bioavailability is the result of the active transport of amino acid chelates from the digestive tract and into the blood stream. In other words, the chelated mineral ions are absorbed through the intestinal lining and into the blood stream, utilizing the amino acids as active transport carriers. More specifically, amino acid chelates are absorbed intact by mucosal cells in the intestines through active transport as is disclosed in U.S. Pat. No. 4,863,898. Because inorganic calcium salts are ionic, they cannot make use of this active transport mechanism, thereby limiting absorption. Therefore, ingested inorganic calcium salts are less bioavailable than the corresponding calcium amino acid chelates. This is in part due to the fact that competition of ions for active sites and the resulting suppression of one nutritive mineral element by another are both avoided.
It has been documented that amino acid chelates can be prepared from metal ions which do not come from soluble salts. U.S. Pat. Nos. 4,599,152 and 4,830,716 both disclose methods of preparing pure amino acid chelates using metal sources other than soluble metal salts. Additionally, in U.S. Pat. No. 5,516,925, methods of preparing amino acid chelates having improved palatability are also disclosed.
Dairy products and oleaginous foods such as cheese, yogurt, ice cream, cream, milk, margarine, oils, etc., are an important part of the human diet and have traditionally been recognized as good sources of calcium. For example, fresh skim and whole milk both contain approximately 118 mg of calcium per 100 g of milk. As such, milk is advantageously consumed by those persons who may be most in need of an adequate calcium intake including people who are dieting and women who are pregnant or middle aged.
Though most dairy products are naturally good sources of calcium, fortification of dairy products with additional calcium is not a new concept. In U.S. Pat. No. 4,784,871, a calcium fortified yogurt is disclosed. In that patent, an acid soluble salt is added to the fruit flavoring prior to combining the flavoring with the yogurt base. The preferred calcium salt used is tricalcium phosphate, dicalcium phosphate, and hydrates thereof. Further, the amounts used are visually undetectable. Additionally, in U.S. Pat. No. 5,449,523, a calcium fortified yogurt is disclosed. In that patent, the calcium source is added to the yogurt milk base prior to pasteurization without undesirable precipitation. Specifically, the process comprises preparing a yogurt base mix comprised of a fermentable dairy ingredient, a calcium source, a chelating agent, and/or an alkaline agent. The chelating and/or alkaline agents are added in amounts to keep the pH of the yogurt base mix above 6.7 prior to pasteurization. The preferred chelating agents are alkali metal citrates which have the primary task of moderating the pH level.
As mentioned, there are some practical difficulties encountered when incorporating calcium into dairy products, particularly in more fluid products such as milk. These problems exist because most calcium fortificants have very low solubility in dairy products. For example, in milk, up to 60-70% of the calcium exists as insoluble colloidal calcium phosphate associated with casein micelles. Added calcium salts tend to settle out, frustrating attempts to maintain uniform dispersions during manufacturing. This settling often alters the texture of the product. In U.S. Pat. No. 5,397,589, this problem is addressed by providing calcium fortified powdered milk products. The patent alleges improved dispersibility in an aqueous media. Essentially, calcium is blended with a milk product. The calcium fortified mixture is cooled to a temperature so that lactose crystallization is initiated. The product is then dehydrated to form a dry powder that is more easily dispersible in an aqueous media. However, this is a process for the manufacture of dehydrated milk. Once hydrated, there are still difficulties in keeping the calcium source suspended in the aqueous media.
Therefore, there is a great need to provide a bioavailable calcium source for dairy products and oleaginous foods which have improved palatability and stability. This is accomplished by the calcium amino acid chelate complexes of the present invention.